The present invention relates generally to the RF (radio frequency) front-end of a mobile terminal and, more particularly, to the RF front-end for a multi-band mobile terminal.
Current trends in the architecture and design of mobile phones are based on multi-band and multi-mode operation. These trends could affect all functional blocks of mobile phone architecture including the RF front-end. At the same time, the development of mobile phones is moving toward high integration of components in order to reduce the manufacturing cost as well as the size of the mobile phone. The implementation of several bands at different frequencies into one mobile phone gives rise to many technical challenges. Typically, the RF front-end architecture and the integrated circuit linking to the front-end are specially designed for each band. The integrated circuit is usually an RF-ASIC (application specific integrated circuit), which includes one or more mixers for down-converting received RF signals to the intermediate frequencies (IF), or for up-converting IF signals to RF frequencies for transmission. The front-end typically includes an antenna, one or more Rx filters and an antenna switch module for mode selection, as shown in FIG. 1. The low noise amplifiers (LNAs) necessary for strengthening the received signals are either discrete components or they are components integrated into the RF-ASIC. The Rx filters between the antenna and the LNA are either discrete components or they are included in the antenna switch module. For some frequency band combinations, the integration of Rx filters into the antenna switch module (ASM) is possible but costly. Such integration restricts the control currents to about 10 mA, and, consequently, the insertion loss in the ASM is relatively high. For other frequency band combinations, the filters and switches in the ASM do not have adequate isolation, especially when the Tx and Rx bands overlap. For example, in a mobile phone that is capable of operating in both PCS1900 and DCS 1800 bands, the PCS1900 Tx frequencies (1850-1910 MHz) and the DCS1800 Rx frequencies (1805-1880 MHz) overlap in the frequency range of 1850-1880 MHz. In the front-end design such as that shown in FIG. 1, the isolation between PCS 1900 Tx and DCS 1800 Rx components is only about 20 to 30 dB, and the leakage power at the bond wire connecting the 1800 MHz Rx amplifier in the RF-ASIC and the bandpass filter in the ASM is approximately 0 to +10 dB. Band overlapping makes this frequency band combination problematic. Similarly, the WCDMA Tx frequencies and the PCS 1900 Rx frequencies overlap. As a result, a significant amount of the Tx signal leaks directly to the input of the Rx LNA. If the LNAs are disposed in the RF-ASIC, the signal present at the bond wires or at the inputs of the RF-ASIC can leak to other parts of the ASIC due to cross-talk. The leakage power can result in intolerably large phase errors in the Tx, for example. One remedy to this problem is to add diodes or transistors to the Rx lines of the problematic Rx paths in order to increase isolation, but this will result in increased cost, current assumption and hardware area.
Furthermore, when the band combination involves a time division multiple access standard (such as GSM) and frequency or coded multiple access standard (such as CDMA where both the Rx and Tx are active at the same time), the front-end requires a duplex filter. The specifications for such duplexers are very stringent. Such duplexers can be realized with ceramic filters, SAW or BAW-based filters. The ceramic filters are large in size and the SAW or BAW-based filters are costly. Thus, the combination of a GSM-like standard and a CDMA-like standard remains a challenge.
It is advantageous and desirable to provide a versatile radio-frequency front-end for use with a radio-frequency application-specific integrated circuit (RF-ASIC) in a multi-band mobile phone. The front-end is designed to avoid the aforementioned problems associated with the current front-end design approach.
It is a primary object of the present invention to provide a versatile RF front-end architecture that would make it easier to re-use an RF-ASIC (application specific integrated circuit), for different band combinations. It is another object of the present invention to provide a method and front-end device for improving the isolation in an antenna system when the transmission frequency band and the receiving band overlap. It is yet another object of the present invention to reduce the cost of producing RF-front-end components and large RF-ASICs. These objects can be achieved by adopting a function-oriented manufacturing approach, wherein the filters, amplifiers, and possibly mixers, are fabricated separately from other signal processing components. In the modular approach according to the present invention, electronic components in a front-end module, such as low-noise amplifiers, that require the demanding silicon bipolar process are fabricated separately from those components in RF-ASICs that can utilize most optimized process for the required functions. When the transmission frequency band and the receiving band overlap, the present invention uses a receiving antenna and a transmitting antenna separately connected to a receiver and a transmitter, instead of an antenna switch module with a duplexer, thereby improving the isolation in the antenna system.
Thus, according to the first aspect of the present invention, there is provided a radio-frequency front-end (100) for use with a radio-frequency signal processor (200) in a multi-band mobile terminal, the mobile terminal capable of operating in a plurality of frequency bands including a first frequency band and a different second frequency band, the front-end adapted to convey signals to and from the signal processor via a connection means (150), wherein the mobile terminal comprises:
an antenna system (10);
a first receiver (522) for receiving first signals in the first frequency band, from the antenna system;
a second receiver (523) for receiving second signals in the second frequency band from the antenna system;
a first transmitter (531) for providing third signals in the first frequency band to the antenna system for transmission; and
a second transmitter (532) for providing fourth signals in the second frequency band to the antenna system for transmission. The radio-frequency front-end is characterized in that
the antenna system comprises:
a first receiving antenna (12a, 12b), operable in the first frequency band and operatively connected to the first receiver (522), for allowing the first receiver to receive the first signals;
a second receiving antenna (12c, 12d), operable in the second band and operatively connected to the second receiver (523), for allowing the second receiver to receive the second signals;
a first transmitting antenna (12g), operable in the first band and operatively connected to the first transmitter (531), for transmitting the third signals.
a second transmitting antenna (12h), operable in the second band and operatively connected to the second transmitter (532), for transmitting the fourth signals. The front-end is further characterized by:
a first frequency filter (322), operatively connected to the first receiver (522) and the first receiving antenna (12a, 12b), for frequency filtering the first signals;
a second frequency filter (323), operatively connected to the second receiver (523) and the second receiving antenna (12c, 12d), for frequency filtering the second signals;
a third frequency filter (324), operatively connected to the first transmitter (531) and the first transmitting antenna (12g), for frequency filtering the third signals; and
a fourth frequency filter (325), operatively connected to the second transmitter (532) and the second transmitting antenna (12h), for frequency filtering the fourth signals.
Advantageously, the front-end further comprises:
a first down-converting element (553, 554), operatively connected to the first receiver (522), for down-converting the first signals for providing down-converted first signals to the signal processor; and
a second down-converting element (555, 556), operatively connected to the second receiver (523), for down-converting the second signals for providing down-converted second signals to the signal processor.
Preferably, the frequency filters are bulk acoustic wave filters.
Preferably, the first and second frequency filters are balanced filters.
According to the present invention, when the plurality of frequency bands further includes a third frequency band, and the mobile terminal further comprises:
a third receiver (521) for receiving fifth signals in the third frequency band from the antenna system; and
a third transmitter (533) for providing sixth signals in the third frequency to the antenna system for transmission, the front-end is further characterized in that
the antenna system further comprises:
a third receiving antenna (12e, 12f), operable in the third band and operatively connected to the third receiver (521), for allowing the third receiver to receive the fifth signals; and
a third transmitting antenna (12i), operable in the third band and operatively connected the third transmitter (533), for transmitting the sixth signals, and further characterized by
a fifth frequency filter (321), operatively connected to the third receiver (521) and the third receiving antenna (12e, 12f), for frequency filtering the fifth signals; and
a sixth frequency filter (326), operatively connected to the third transmitter (533) and the third receiving antenna (12i), for transmitting the sixth signals. The sixth frequency filter may be fed by a mixer or up-converting element (210n).
Alternatively, when said plurality of frequency bands further includes a third frequency band, and the mobile terminal further comprises:
a third receiver (521) for receiving fifth signals in the third frequency band from the antenna system;
a third transmitter (533) for providing sixth signals in the third frequency to the antenna system for transmission, the front-end is further characterized in that
the first receiving antenna (12a, 12b) is also operable in the third frequency band;
the antenna system further comprises a third transmitting antenna (12i), operable in the third band and operatively connector the third transmitter (533), for transmitting the sixth signals, and is further characterized by
a fifth frequency filter (321), operatively connected to the third receiver (521) and the first receiving antenna (12a, 12b), for frequency filtering the fifth signals;
a sixth frequency filter (326), operatively connected to the third transmitter (533) and the third receiving antenna (12i), for frequency filtering the sixth signals; and
a phase shifter (14), operatively connected between the first frequency filter (322) and the fifth frequency filter (321) for matching the first and fifth frequency filters.
According to the second aspect of the present invention, there is provided a method of improving the flexibility in use of a radio-frequency front-end (100) with a radio-frequency signal processor (200) in a multi-band mobile terminal, the mobile terminal capable of operating in a plurality of frequency bands including a first frequency band and a different second frequency band, the front-end adapted to convey signals to and from the signal processor via a connection means (150), wherein the mobile terminal comprises:
an antenna system (10);
a first receiver (522) for receiving first signals in the first frequency band, from the antenna system;
a second receiver (523) for receiving second signals in the second frequency band from the antenna system;
a first transmitter (531) for providing third signals in the first frequency band to the antenna system for transmission; and
a second transmitter (532) for providing fourth signals in the second frequency band to the antenna system for transmissions, said method characterized by
providing in the antenna system a first receiving antenna (12a, 12b), operable in the first frequency band and operatively connected to the first receiver (522), for allowing the first receiver to receive the first signals, and a first frequency filter (322), operatively connected to the first receiver (522) and the first receiving antenna (12a, 12b), for frequency filtering the first signals;
providing in the antenna system a second receiving antenna (12c, 12d), operable in the second band and operatively connected to the second receiver (523), for allowing the second receiver to receive the second signals, and a second frequency filter (323), operatively connected to the second receiver (523) and the second receiving antenna (12c, 12d), for frequency filtering the second signals;
providing in the antenna system a first transmitting antenna (12g), operable in the first band and operatively connected to the first transmitter (531), for transmitting the third signals, and a third frequency filter (324), operatively connected to the first transmitter (531) and the first transmitting antenna, for frequency filtering the third signals; and
providing in the antenna system a second transmitting antenna (12h), operable in the second band and operatively connected to the second transmitter (532), for transmitting the fourth signals, and a fourth frequency filter (325), operatively connected to the second transmitter (532) and the second transmitting antenna (12h), for frequency filtering the fourth signals.
Advantageously, the method is further characterized by
providing a first down-converting element (553, 554), operatively connected to the first receiver (522), for down-converting the first signals for providing down-converted first signals to the signal processor. Advantageously, the method is further characterized by
providing a second down-converting element (555, 556), operatively connected to the second receiver (523), for down-converting the second signals for providing down-converted second signals to the signal processor.
Preferably, when said plurality of frequency bands further includes a third frequency band, and the mobile terminal further comprises:
a third receiver (521) for receiving fifth signals in the third frequency band from the antenna system; and
a third transmitter (533) for providing sixth signals in the third frequency to the antenna system for transmission, the method is further characterized by
providing in the antenna system a third receiving antenna (12e, 12f), operable in the third band and operatively connected to the third receiver (521), for allowing the third receiver to receive the fifth signals, and a fifth frequency filter (321), operatively connected to the third receiver (521) and the third receiving antenna (12e, 12f), for frequency filtering the fifth signals; and
providing a third transmitting antenna (12i), operable in the third band and operatively connected to the third transmitter (533), for transmitting the sixth signals, and a sixth frequency filter (326), operatively connected to the third transmitter (533) and the third receiving antenna (12i), for transmitting the sixth signals.
Alternatively, when said plurality of frequency bands further includes a third frequency band, and the mobile terminal further comprises:
a third receiver (521) for receiving fifth signals in the third frequency band from the antenna system;
a third transmitter (533) for providing sixth signals in the third frequency to the antenna system for transmission, the method is further characterized in that
the first receiving antenna (12a, 12b) is also operable in the third frequency band, and
the antenna system further comprises a third transmitting antenna (12i), operable in the third band and operatively connected to the third transmitter (533), for transmitting the sixth signals, and the method is further characterized by
providing in the antenna system:
a fifth frequency filter (321), operatively connected to the third receiver (521) and the first receiving antenna (12a, 12b), for frequency filtering the fifth signals;
a sixth frequency filter (326), operatively connected to the third transmitter (533) and the third receiving antenna (12i), for frequency filtering the sixth signals; and
a phase shifter (14), operatively connected between the first frequency filter (322) and the fifth frequency filter (321) for matching the first and fifth frequency filters.
The present invention will become apparent upon reading the description taken in conjunction with FIGS. 2 to 6.